The fuel consumption and emission values of modern combustion engines are substantially influenced by the time of injection and the duration of the injection of the fuel into combustion cylinders of the combustion engine. Complete combustion is guaranteed only if, inter alia, the same quantity of fuel is injected into all of the combustion cylinders. Otherwise there is an increased discharge of unburnt hydrocarbons.
Furthermore the injection must be executed in accordance with a predefined timing cycle. If an injection deviates from this timing cycle, this leads to misfires which the driver perceives as unpleasant jerking, in particular when the engine is idling.
For this reason engine management systems are provided in conjunction with injection valves which precisely control both the injection point and the injection duration or, as the case may be, the end of the injection.
Injection valves having pump-nozzle systems store fuel in the injection valve under high pressure. For an injection period a nozzle valve is opened and some of the fuel is injected out of the injection valve.
Due to manufacturing factors the injection valves exhibit different injection characteristics. These differences are accepted as tolerances, since a more precise manufacture of the injection valves would lead to disproportionately high overheads. On the other hand these tolerances are a contributory factor to the less than optimal operation of the combustion engines.